The present invention relates chiefly to a pulley, which entrains a belt, such as the timing belt or a belt for driving an auxiliary machine, driven by an automobile engine.
Pulleys are used for belts, such as the timing belts and belts for driving auxiliary machines, driven by automobile engines and disposed to increase the wrapping angle of the belt and impart a suitable tension to the belt. FIG. 6 shows an example of arrangement of a timing belt, wherein an endless belt E is entrained around a driving pulley A fixed to a crank shaft, driven pulleys B, B fixed on cam shafts, a tensioner pulley C rotatably mounted on a fixed shaft and an idler pulley D. Of these pulleys, the pulleys C and D mounted on fixed shafts are usually bearing-equipped pulleys having bearings installed in the inner portions thereof.
If the aforesaid bearing-equipped pulleys are driven in a cold climate, they sometimes produce a peculiar sound (whistle sound) depending on the pulley specifications and operating conditions. Such peculiar sound in a cold climate, or the so-called cold peculiar sound, does not always occur in the market; rather, it depends on the temperature, etc., and in Japan it occurs only in very limited districts (Hokkaido, etc.). Further, it occurs for a very short time (1 minute at most) following the start of the engine of an automobile; thereafter, there is no such sound. Further, the sound is frequently produced when a single row deep groove ball bearing is used as the ball bearing, and the rate of occurrence decreases when a double row angular ball bearing is used.
Cold peculiar sound has such complicated properties and can hardly be reproduced, a fact which accounts for the fact that its cause of occurrence has not yet been clearly analyzed. Furthermore, the pulleys used in automobiles are operated at high temperature and at high speed and their durability is also an important property, so that a measure which leads to a lowering of durability cannot be adopted.
For this reason there is provided at present no effective means worthy of mention which can be used as a cold peculiar pulley sound preventive measure.
Conventionally, as a cold peculiar sound preventive measure, investigations are made as to the use of a grease which is superior in low temperature properties (a grease which, even in a cold climate, forms oil films uniformly on the areas of contact between the rolling bodies and the raceway surfaces of the inner and outer rings). This preventive means is intended to effectively suppress the occurrence of cold peculiar sound by enhancing the lubricating performance of grease in a cold climate, and a substantial effect can be expected. However, since the NLGI consistency number of grease decreases, there is anxiety about the lubricating performance in a hot climate, possibly leading to a lowering of durability.